Stratification and charging rate, Some help?

[paulcheung]

I am try to understand the stratification and the relation to charging rates. I know C/12 to C/8 is the rate we should charged the FLA batteries. How does stratification affect the batteries when they are charged under C/12 rate? how long become a problem? less than a day? or more than a day?

When charged the batteries under C/12 rate like C/20 during the day and in the near end of the day, the voltage go over the gassing voltage like 60 volt for 48 volt system, the batteries gassed up, would that take care of the stratification?

Thank you.

[Sunking]

Paul stratification is caused primarily from two functions. The main issue is sitting still in a static position without receiving a full saturation charge. What that means is getting the battery fully charged until it reaches the gassing voltage. It is the gassing that mixes the electrolyte.

Can that happen at a C/20 charge rate? Yes it can but that assumes you can apply a C/20 rate long enough to ever reach gassing or saturation voltage and leaving it there long enough to do any good. How many solar systems can do that? NONE.

This is why any off-grid solar system must have a generator that can apply maximum charge rate at Equalization voltage which is a controlled over charge forcing the batteries to gas.

[paulcheung]

Paul stratification is caused primarily from two functions. The main issue is sitting still in a static position without receiving a full saturation charge. What that means is getting the battery fully charged until it reaches the gassing voltage. It is the gassing that mixes the electrolyte.

Can that happen at a C/20 charge rate? Yes it can but that assumes you can apply a C/20 rate long enough to ever reach gassing or saturation voltage and leaving it there long enough to do any good. How many solar systems can do that? NONE.

This is why any off-grid solar system must have a generator that can apply maximum charge rate at Equalization voltage which is a controlled over charge forcing the batteries to gas.

How long do it need to gas up so the electrolyte get mix up at C/20 charge rate? 15 minutes? one hour? or more? When charge at C/10 at low voltage at around 50 volts, does that mixing the electrolyte in the early part of charge cycle?

Thank you.

[Sunking]

How long do it need to gas up so the electrolyte get mix up at C/20 charge rate? 15 minutes? one hour? or more?

Paul we got to get your mind wrapped around around batteries. You don't have a grasp yet. Charge rate has nothing to do with gassing at least not in the sense of a C/X charge rate. All C/X charge rate means is a constant charge current algorithm up to a SET POINT and the SET POINT will be a Voltage value below gassing. Constant Current algorithm only applies to what is called the BULK charging phase. Now with that said if you were to use Constant Current above the gassing voltage you would boil the acid right out of a battery or rupture the valves in a Sealed battery. So you gotta get your mind around Bulk, Absorb, Float, and Equalize charging phases. In a nut shell Bulk is constant current algorithm, and all the others are Constant voltage with current limit. Burn that into your BRAIN

Let's talk about BULK for a minute because this is where the C/X rate is applied. C = the AH rating of a battery specified at the 20 hour discharge rate. X = Time in Hours. For example a 100 Amp Hour battery. C/20 charge rate on a 100 AH battery = 100 Amp Hours / 20 Hours = 5 Amps. A lead acid battery that is discharged below 20% DOD can be charged at very high rates of up to 1C. 1C on a 100 AH battery is 100 amps. No manufacture would ever recommend that because significant heating starts to occur at rates above C/8. Thus the limitation you hear spoken of as the upper limit for flooded lead acid batteries.

So here is what BULK charge does. It charges the battery as fast as we can up to 80 to 90 % Saturation Voltage. The BULK termination phase end when the battery voltage reaches 80 to 90% saturation voltage which is below is below GASSING VOLTAGE. So the battery never gasses during the BULK STAGE. Burn that in your BRAIN. What is the Saturation voltage. It depends on the battery temperature and alloy in which the battery is made of. Keep this in mind as this is where Temperature Compensation comes into play.

What you and everyone else reading thus far want to know is how do we get to 100% SOC. Well if using solar will likely never will happen unless you have a generator or commercial AC power source with a good quality AC charger made for cycled batteries. To get from 80 to 90% where BULK ends up to 100% takes a SATURATION CHARGE aka ABSORB CHARGE. Yes your charge controller most likely has a ABSORB stage, but is useless for most people. Why you ask? Because it take 4 to 8 hours to go from 80% to 100%. With Solar you do not have that much Sun. What is ABSORB? It is a CONSTANT VOLTAGE with CURRENT LIMIT. Bulk stage ends when voltage on a 12 volt battery reaches around 14 volts. At that point the Charger ups the voltage to about 15 to 16 volts depending on TEMPURTURE. Initially when that happens the current shoots up to whatever BULK current was which is the CURRENT LIMIT. When the battery terminal voltage equals the ABSORB SET POINT VOLTAGE the current begins to taper off to zero amps, but the voltage is held at a CONSTANT LEVEL.. What voltage is ABSORB SET POINT? It is the battery GASSING VOLtAGE. Burn that into your brain. What is the GASSING VOLTAGE? Beats me as it depends on TEMPERATURE and Alloy. It can be as high as 16.5 volts at -20 C to as low as 13.5 volts @ 50C.

So here is what you want to know Paul, when do you terminate ABSORB charging phase or 100% charged. It ends when the current tapers down to 3 to 5% of C. So on a 100 AH battery when the current tapers down to 3 to 5 amps. How long does it take? a long time of about 6 hours average. Can you do that with solar? Hell no. It takes a genny or commercial AC power.

So what do you do? Well to start with set your charge controller to Bulk = Absorb = Manufactures Temperature Compensated ABSORB Voltage using a battery temp sensor installed on the PILOT CELL somewhere in the middle of the string away from the ends. Then about once in a week or two use your genny or commercial AC power with a good quality 4 stage battery charger to go through a complete full 2 stage charge of completing Bul and Absorb until it switches to Float Mode. When dictated by specific gravity apply a Equalize charge with genny or commercial AC power.

BURN all that into your brain Paul.

[paulcheung]

Gotta, Thank you to take the time to explain in detail.

[Sunking]

Gotta, Thank you to take the time to explain in detail.

You are more than welcome.

[Mike90250]

While my system is not Lead acid, it does gas, but according to battery voltage. Below 61 volts, there is no gassing, but above 61, the gassing starts. Opening the door to the battery shed while charging, it sounds like a room full of hissing snakes from all the bubbles. It's the action of the bubbles swirling the water around, that de-stratifys the batteries. 10 minutes is not enough time, 1 hour is probably better to remix the electrolyte.
And yes, I go though a lot of distilled water.